1. Technical Field
The present invention relates to a scanning electron microscope having a monochromator for monochromatizing the energy of an electron beam.
2. Background Art
In a recent scanning electron microscope (SEM: Scanning Electron Microscope), for the purpose of preventing a semiconductor sample or the like from being electrically charged by an electron beam, such electron beam having a low-voltage energy of several keV or lower is often used. In such a low-voltage SEM, an energy width specific to an electron source is relatively large with respect to electron-beam voltage energy. Thus, it is problematic in that a sufficiently small spot diameter cannot be obtained, since blurring is caused due to so-called chroma aberration. In order to solve such a problem associated with the low-voltage SEM, JP Patent Publication (Kokai) No. 2004-214111 A, for example, proposes a scanning electron microscope having a monochromator that selectively passes only an electron beam in a desired energy range.
Based on the monochromator and the SEM proposed in JP Patent Publication (Kokai) No. 2004-214111 A, using a first focusing lens, the electron beam is caused to be incident so that a real image of the electron source is formed on the intersection of a linear optical axis of the electron beam with a symmetry plane of the monochromator. The electron beam is then deflected away from the linear optical axis of the electron beam through a sectorial magnetic field, and the deflected electron beam is further deflected through a sectorial electrical field, whereby energy dispersion is caused. The energy of the electron beam is monochromatized by passing the electron beam through a slit placed in an energy dispersion surface.